Need Help: Variable transfer to other class

I'm new to c++ and I'm writing a 2D game with SDL right now and i want to make a game where you're being followed by a tornado. So you can move ans the tornado move towards you. But when I use the x coordinates of the boy in the move section of the tornado it sais that te xboy is not declared so I can i do that

after this, I have the other functions and then I create the Tornado class

Code:

//The Tornado that will move around on the screen
class Tornado
{
private:
//The X and Y offsets of the Tornado
int xtor, ytor;
//The velocity of the Tornado
int xVeltor, yVeltor;
public:
//Initializes the variables
Tornado();
//Moves the Tornado
void move();
//Shows the Tornado on the screen
void show();
};
Tornado::Tornado()
{
//Initialize the offsets
xtor = 800;
ytor = 400;
//Initialize the velocity
xVeltor = 0;
yVeltor = 0;
}
void Tornado::move()
{
//Move the Tornado left or right
xtor += xVeltor;
//If the Tornado is at the right side of the boy
if( xtor > xboy )
{
//move to the left
xVeltor = -5;
}
//If the Tornado is at the left side of the boy
if( xtor < xboy )
{
//move to the left
xVeltor = 5;
}
//Move the Tornado up or down
ytor += yVeltor;
//If the Tornado is above the boy
if( ytor < yboy )
{
//move to the left
yVeltor= 5;
}
//If the Tornado is under the boy
if( ytor > yboy )
{
//move to the left
yVeltor = -5;
}
}

The game works when I place a number in stead of xboy and yboy but then the tornado moves towards that point and then stays right there.

"Simplicity does not precede complexity, but follows it." -- Alan Perlis
"Testing can only prove the presence of bugs, not their absence." -- Edsger Dijkstra
"The only real mistake is the one from which we learn nothing." -- John Powell